(二)现在完成时(Present Perfect Tense)

　　1. 已完成用法： 表示动作在过去某一不明确的时间已完成，强调对现在的影响，这一用法常不带时间状语或可与不明确的时间状语连用，如： already，yet，ever，just，never。

　　例句： I have excluded him because, while his accomplishments may contribute to the solution of moral problems, he has not been charged with the task of approaching any but the factual aspects of those problems. (2006年第48题)

　　分析： 该句是复合句。在because引导的原因状语从句中又加入了由while引导的让步状语从句。

　　译文： 我之所以将他(普通科学家)排除在外，是因为尽管他的成果可能有助于解决道德问题，但他承担的任务只不过是研究这些问题的事实方面。

　　例句：The same dramatic technological changes that have provided marketers with more (and more diverse) communications choices have also increased the risk that passionate consumers will voice their opinions in quicker, more visible, and much more damaging ways. (选自2011年Text 3)

　　分析：该句是复合句。主句的主干部分是The same dramatic technological changes have also increased the risk。that have provided marketers with more (and more diverse) communications choices是一个定语从句，修饰changes;that passionate consumers will voice their opinions in quicker,more visible, and much more damaging ways是risk的同位语从句，介词短语in quicker, more visible, and much more damaging ways在该同位语从句中作状语，表示方式，修饰谓语动词voice。

　　译文：同样是这些重大的技术变革，在给营销商带来更多的(以及更多样化的)传播渠道选择的同时，也增加了风险，那就是热情洋溢的消费者将会以更快、更明显和更具破坏性的方式表达他们的观点。

　　2. 未完成用法： 表示动作从过去某时开始持续到现在，还有可能持续下去，强调持续性，这一用法要带表示一段时间的状语，如： recently, these days, for 3 years, since 2000, over the past等。

　　例句： For example, it has long been known that total sleep deprivation is 100 percent fatal to rats, yet, upon examination of the dead bodies, the animals look completely normal.

　　分析： 该句是复合句。

　　译文： 比如，人们早已知道，完全剥夺其睡眠对老鼠而言绝对是致命的。然而，在检验动物尸体时，那些动物看起来是完全正常的。

　　例句： Since the dawn of human ingenuity, people have devised ever more cunning tools to cope with work that is dangerous, boring, burdensome, or just plain nasty. (选自2002年Text 2)

　　分析： 该句是复合句。句中定语从句that is dangerous，boring，burdensome...修饰work， since...在句中作状语。

　　译文： 自从人类具有了独创性以来，人们就发明了愈加精巧的工具来处理那些危险、无聊、麻烦或者仅仅是令人讨厌的工作。

　　3. 现在完成时用于时间或条件状语从句中表示将来完成的动作。

　　例句： Ill help you when I have finished my work. I will return the book if I have finished it.

　　4. 下列表达方式后要用现在完成时。

　　This (That/It) is the first (second...)...

　　This (That/It) is the best (finest/worst/most interesting...)...

　　例句： This is the first time that China has had such negotiations with a G7member, the official said.

　　译文： 该官员说，这是中国与七国集团成员首次进行这样的谈判。

　　例句： This is the first time that he has felt really relaxed for months.

　　译文： 几个月来他第一次真正感到放松。

　　注意： 如果主句动词表示过去时间，从句常用过去完成时;如果主句动词表示将来时间，从句仍使用现在完成时。

　　例句： It was the best picture that she had seen.

　　It will be the best picture that she has seen.

　　5. 有些时间状语常用于现在完成时态。

　　如：

　　up till nowso farat (for) the past (last) years

　　in recent yearsup to present

　　例句： For the past several years, the Sunday Newspaper supplement Parade has featured a column called“Ask Marilyn”. (选自2007年Text 2)

　　分析： 该句是简单句，其中called“Ask Marilyn”作后置定语，修饰a column。

　　译文： 在过去的几年里，《展示杂志》周日增刊上出现了一个叫做“向玛瑞林提问”的特色专栏。

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